New spec-based func for creating adjacency lists.
Convert all test suites to new spec approach
Add missing GraphSpec methods for mutability
Convert test suite fixtures to spec-based.

These *really* need to be reimplented with test logic, not just reusing
adjacency lists. ugh.
Comment out benchmarks, for now
Remove the old builder style entirely, woot
Rename al_builder.go to builder.go
Move builder constants into builder.go
goimports